JPS6142185A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a cavity surface vertical and flat by chemical etching by a method wherein a laser is further epitaxialy grown on the uppermost layer of epitaxial layers, and a stripe photo mask having a parallel edge is formed thereon. CONSTITUTION:An N type GaAlAs clad layer 2, a GaAs active layer 3, a P type GaAlAs clad layer 4, and a P type GaAs cap layer 5 are successively grown on an N type GaAs (100) substrate 1; thereafter, the layer 5 is provided with a GaAlAs layer 7, and the stripe photo mask 6 is formed on the layer 7 along the <011> direction. Then, etching is carried out to the substrate 1 through the mask 6. At this time, etching with the AlAs mixed crystal ratio of the layer 7 set at 0.5 and that of the layers 2 and 4 set at 0.4 produces a cavity surface vertical and flat.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a compound semiconductor device mainly composed of GaAs and GaAIAa, particularly a semiconductor laser device.

Structures of Conventional Examples and Their Problems Chemical etching of GaAs and GaAIAs-based compound semiconductors has been studied for some time, and there have been many reports on their etching characteristics. Etchant, etching rate, GaAs; J) or GaA
Details of lAs selective etching solution, etching profile, etc. are known. Using such chemical etching technology, surface treatment of GaAs and GaA
Selective etching of wafers consisting of s/G a I A s has been performed. Furthermore, such techniques have also been used to fabricate cavity surfaces for semiconductor lasers and the like.

Semiconductor lasers generally have a cavity surface formed by the cleavage method, but when attempting to integrate a semiconductor laser and elements such as a detector and drive circuit into a monolink, such as in an optical IC, the cleavage method cannot be used at all. Can not. For this purpose, wet etching methods such as chemical etching methods and dry etching methods such as active ion etching (RIE) are being studied. Chemical etching is superior in terms of mass production and reliability, and because of its ease, various methods have been tried to fabricate the cavity surface. Problems in producing a cavity surface by chemical etching are the perpendicularity of the cavity surface and the flatness of the surface.

FIG. 1 shows the relationship between the inclination θ of the cavity surface and the normalized reflectance. As can be seen from this, the reflectance decreases by as much as 60% when the cavity surface is tilted by only about 6 degrees, which leads to an increase in the threshold value and a decrease in the external differential quantum efficiency. Furthermore, the reflectance is significantly reduced due to the roughness of the cavity surface.

Due to these problems, lasers fabricated by conventional chemical etching methods have a higher threshold current density than cleavage method liquids, making continuous oscillation extremely difficult.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a method for manufacturing a semiconductor laser device in which a vertical and flat cavity surface is formed by a chemical etching method.

Structure of the Invention The present invention provides an epitaxial layer comprising an active layer containing at least Ga and A8 as a composition and a cladding layer sandwiching the active layer on a single crystal substrate containing at least Ga and A8 as a composition. When fabricating a semiconductor laser device using the above-mentioned method, one more layer is epitaxially grown on the top layer of the above epitaxial layer, and a <100> layer is formed on this layer.
, (110>) or an equivalent direction thereof, and chemical etching is performed to the single crystal substrate through the photomask to form a cavity surface. This is the manufacturing method.

Embodiments 12 Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 2 shows Ga1 on a (100) GaAs substrate.
, A/, shows experimental results regarding the inclination angle of the etching profile when the As layer is grown and etched through a slice-shaped mask along the <011) direction. The tilt angles θ1 and θ2 vary greatly depending on the AlAs mixed crystal ratio X. When the value of X is around 0.2 and 0.4, the tilt angle θ1 is about 900.

On the other hand, the angle θ2 generated at the interface with the GaAs substrate is x<o,
1 and X-0, 4, it is almost o. X
If we pay attention to the vicinity of 0.4, θ1~900 and θ2~O
0, the etched end surface becomes a vertical and flat surface.

If this result is applied to a semiconductor laser, a cavity surface almost equivalent to a cleavage surface can be obtained. As an example, we will explain the fabrication method by setting the A I A a mixed crystal ratio of the cladding to 0.4 based on the results shown in FIG. 2.As shown in FIG. Board 1
n-type Gao, s Alo, 4A8 cladding layer 2 on top
, GaAs active layer 3p type Gao, eAJo,
4. The A8 cladding layer 4 and the p-type GaAs cap layer 6 are successively grown.

Semiconductor lasers generally have a four-layer structure like this, and conventional chemical etching methods have been used to remove the top layer, p-type Ga
7 striped mask 6 is placed on the s scan 1 layer 5.
011> direction, and through the mask
Etching was performed up to the aAs substrate 1. This method results in an inverted mesa-like etching profile as shown in FIG. 3, and a vertical cavity surface cannot be obtained.

This can also be explained from the results shown in FIG.

FIG. 4 explains the etching profile from the angles of inclination θ1 and θ2. That is, p-type Ga As
On the first layer s of the can, since θ1-66°0 with respect to the surface, the shape is an inverted mesa with a corner 660 as shown in FIG. 4, and a vertical cavity surface is never obtained. Therefore, in the present invention, a fifth G is formed on the p-type GaAs cap layer 6.
a 1y A l! A As layer 7 is provided (FIG. 6a),
A striped photomask is formed on it along the <oll> direction, and Ga As is passed through the mask.
Etching is performed up to the substrate 1 (FIG. 6b). The conditions for vertically etching the p-type cladding layer 4 and below are 5th G.
a 1-A A ly A A between the s layer 7 and the cladding layer 4
Various methods can be considered depending on the combination of IAs mixed crystal ratios.

As an example of the present invention, the AlAs mixed crystal ratio y of the fifth layer 7 is
=0.5. x of both cladding layers 2 and 4 = 0.4.

1H, SO2:8H202:1H20 (2
Etching was performed up to the substrate 1 under conditions of (0°C). 6th
Since layer 7 will be removed eventually, it is better to perform selective etching with y) set to 0.5.

FIG. 6 shows the etching method 7 of the present invention based on the results shown in FIG.
0 file is explained. 6th Gao, 6A1
The 0.5As layer 7 has an inverted mesa shape with an inclination θ1=660, but at the interface of the p-type GaAs cap layer 5, the slope is 02 to 25°.
becomes. θ1=660. Since θ2=260, p
The end face of the G a As cap layer 6 is already vertical, and since both cladding layers are set to 0.4, the verticality is maintained up to the substrate, similar to the p-type cap layer.

After creating the cavity surface by etching, the 6th Ga
After selectively removing the AIAs layer 7 and forming a positive electrode 8 on the exposed p-type GaAscan 1 layer 6 and a negative electrode 9 on the substrate side, the etched groove is Break 1. Thus, a semiconductor laser device as shown in FIG. 7 is obtained.

In the above embodiment, Ga 1yA l is used as the layer on top of the top layer A.
yA s was used, but this is not necessarily Ga 1yA
It doesn't have to be ly As. In short, any semiconductor single crystal may be used as long as it has a Zn1c Blend structure that has a lattice constant close to that of 1'aAs, which is the fourth layer, and is the same as GaAs. For example, GaAgP, JnGaAs
■-v group compounds such as P can be used depending on the composition ratio.
It is possible to grow a single crystal that matches extremely well with As, and it is possible to produce etching anisotropy. Further, an n-■ group compound having a Zinc Blend structure such as Zn5e, Zn5eTe, ZnTe, or CdTe may be used. These can be easily formed by molecular beam epitaxial method. For example, G a A B o ,s
When Po,5 is used as the fifth layer, Gao,s
Similar to the case using Alo, sA B, pmGao,
It was confirmed that the end face of the 6AJ0.4As crat layer 4 could be etched vertically.

FIG. 8 shows the optical output-current characteristics of the semiconductor laser device shown in FIG. 5. Obtained with very high yield through continuous oscillation, with a typical oscillation threshold of 72 mA (70 mA with the cleavage method)
The differential quantum efficiency is 29 cm per side (30% in the cleavage method).
) and the cleavage method obtained properties with almost no difference.

Effects of the Invention A feature of the present invention is that a mirror cavity surface perpendicular to the bonding surface can be produced by chemical etching. The advantages of obtaining a cavity surface equivalent to a cleavage surface using the chemical etching method are that it is easy to integrate other elements on the same substrate, that short cavity lasers can be fabricated, and that the formation of a protective film on the laser end face is done in batch processing. The practical effects of this technology are significant, such as the fact that it can be done with a wafer, and the characteristics can be inspected on the wafer itself.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the inclination of the cavity surface and the reflectance, and FIG. 2 is a diagram showing the relationship between the inclination of the cavity surface and the reflectance. A
Figures 3a and 3b show the inclination angle of the etched end face when the lxAs layer is grown and etched through a striped mask along the <011> direction. FIG. 4 is a diagram showing the manufacturing method of the cavity surface to be etched, and FIG. 6a is a diagram for explaining the inclination of the end surface. b is a diagram showing a method of manufacturing a cavity surface by etching of a semiconductor laser according to the present invention, FIG. 6 is a diagram for explaining the inclination of the end face, and FIG. 7 is a perspective view of a semiconductor laser manufactured by the manufacturing method of the present invention. FIG. 8 is a diagram showing the optical output-current characteristics. 1...N-type GaAs+ (100) substrate, 2...
...n-type GaO, 6"0.4" cladding, 3-=
・-GaAs active layer, 4...p-type Ga□, 6A
A! 0. , *A8 cladding layer, 6...p-type G
a A s cap layer, 6...photomask, 7...5th Gao, s Alo, s
As layer, 8...positive electrode, 9...negative electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Fig. 4 f' Fig. 5 Fig. 6 Fig. 1'

Claims (3)

[Claims] (1) A semiconductor laser device in which an epitaxial layer including an active layer containing at least Ga and As as a composition and a cladding layer sandwiching the active layer is formed on a single crystal substrate containing at least Ga and As as a composition. When manufacturing the above epitaxial layer, another layer is epitaxially grown on the top layer of the above epitaxial layer, and on this layer, <100>, <
110> or an equivalent direction thereof, and chemical etching is performed to the single crystal substrate through the photomask to form a cavity surface. . (2) The layer grown on the top layer is GaAs, GaAl
At least Ga such as As, GaAsP, InGaAsP
2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the semiconductor layer is a semiconductor layer containing and As as components. (3) The layer grown on the top layer is ZnTe, CdTe
2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the semiconductor laser device is a II-VI group compound semiconductor such as ZnSe or the like.